Lens system.



BSO-418 j... NEAL Patented lar. I8, |902.

E. F. GRN. LENS SYSTEI.

(Application lnd July 3, 1901.)

(lo Modal.)

2 Sheets-Shoot l.

no. 695,666. Patented mar. la, |902'.

E. 4r. 66ml. LENS SYSTEM.

(Application led July 3, 1901.)

m, wf

Q A l wn uonms reune co. mouma. wnmrmvou, n, c.

UNITED STATES .PATENT OEEIcE.

EDVARD FERDINAND GRN, OF SOUTHVICK, ENGLAND.

LENS SYSTEM.

SPECIFICATION forming part of Letters Patent No. 695,606, dated March18, 1902.

Application filed July 3, 1901. Serial No. 67,028. (No model.)

To all whom it may) concern:

Be it known that I, EDWARD FERDINAND lGRiiN, a subject of the King ofGreat Britain,

residing at Southwick, county of Sussex, En gland, have invented anImproved Lens System, (for which I have made application for LettersPatent in Great Britain under No. 6,194, dated March 25, 1901,) of whichthe following is a specification.

The present invention relates to photographic and other lenses, theobject being to produce a lens system of very wide angle and of greatdepth of eld and primarily great rapidity. i

It is well known that to produce a glass lens of wide 'angle the lensmust comprise a long body of glass. There are three objections to suchalens: iirst, it is impossible to obtain a piece of pure glassabsolutely without flaws and of a length suitable for the purpose;secondly, a lens so produced only forms a clear image of objects in oneplane-that is, it has no depth of field; thirdly, such a body of glassnecessarily absorbs a large percent-age of the actinic rays which passthrough it, and it is unsuitable for the purposes of photography.

According to this invention as applied to a lens system fora telescope,photographic camera, or similar apparatus two or more achromatic lensesare mounted in a tube or cylinder, and the space between the lenses isfilled with a fls'id having as nearly as possible the same refractiveindex as the substance forming. the lenses, the iluids chosen havingpractically no dispersive power of light. Thus by placing two achromaticlenses at a consider- I able distance apart and filling up the spacebetween them with a liquid of the kind vdescribed a long lens of verywide angle will he obtained which will be open to none of the objectionswhich have been applied above to the solid glass lens. The internalconcavities which must exist in all achrornatic lenses are therebyabolished as far as the refraction is concerned; but their achromatizinginfiuence is still retained. By this means the whole available convexityis retained and a lens ofl very short focus and of considerable depth offield is formed.

The accompanying drawings show sectional Y elevations of lensesconstructed in accordance In Figure 1, A A are the achromatic lenses,which may be of the same or of different foci and are mounted at somedistance apart in a tube or holder C, the space between the lenses beingfilled with fluid B. In Fig. 2 a third lens D is shown in addition tothe above, an air-space being left between A and D.

With glass such as is generally employed in the manufacture of lenses ithas been found that cedar-oil or monobromid of p aphthalene possessingn'flyth'es'am'dex of refraction as the glass answers the purpose'gwell;but any iiuid may be employed, so long as it possesses nearly the samerefractiye index as the material of which the lens is formed, providedsuch iiuid, so far as its quality of dispersing rays of light isconcerned, does not materially dier from cedar-oil. Preferably I employa iiuid of such a nature that ordinary changes of temperature do notappreciably affect it.

yBy -employing a fluid of the class above mentioned I am able to producea lens in which all appreciable internal diffraction and reflection areeliminated. The focal distance of the lens combination is considerablyre,

duced, and the effect of thisreduction of the focal length is to givevan image of intense brilliance and capable of producing aphotographicnegative in faint or imperfect light,

where it has'hitherto been impossible to take photographs. A compoundlens formed by this arrangement has a higher aperture than any lenseshitherto constructed, and on account of the high aperture of the lens itis specially adapted for kinematograph or similar .photographic work orfor taking,photographs or observations when the lightavailable is dimorof a low actinic powerthe image being projected through the lenses ontoa photographic or other screen with great IOO system. By its usephotographs may be taken in light in which the objects are just visible'to the human eye-that is to say, stage and moonlight effects-and owingto the rapidity of the lens system rapidly-moving objects can bephotographed in daylight more accurately and producing better resultsthan hitherto. The power of telescopes having the improved lens systemis enormously increased, as hitherto the chief obstacle has been theproduction of object-glasses equivalent in optical effect to glasses ofmuch larger diameter, and such glasses having a short focal length canreadily be constructed according to this invention.

The fluid employed is preierablyrcgedar-olI as it has been found that itabsor s ess ight than glass; but this invention also includes the use ofglycerin, 'monobromin' of naphthalene, sandalwQQd.6l, e5senja] nil of caPaiba, ersubstanceshavingapproximately the sagievin nas the materialforming thalens and ha 'n0' sub- ""M "d my. stantlallyl'thwdaspersmesquaity as cedar-oil.

What I claim as my invention, and desire to secure by Letters Patent,is-

l. In a wide-angle lens system the combination with two achroma'ticlenses at some distance apart of a body of iiuid disposed in 3o thespacebetween the achromatic lenses and having approximately the samerefractive index as the `lenses substantially as and for the purposedescribed.

2. In a wide-angle lens system the combi- 35 nation with two achromaticlensesat some distance apart ofa body of cedar-oil disposed in thespaebetween the lenses and having .approximately the same refractive indexas' EDWARD FERDINAND GRN.

Witnesses: i

JAMES BACN RYE, WILMER-M. HARRIS.

